In the field of electronic equipment, such as a cellular phone, a book-size personal computer and a PDA (personal digital assistance) which all require high-speed communication, a production which realizes higher-speed communication is desired to be provided in a smaller, thinner and lighter form. For this reason, miniaturization of the products in this field is rapidly advancing. Further, these products are also required to have higher performance and multifunctionality in addition to a smaller size. In order to meet the requirements, microminiaturization of a semiconductor device has been accelerated and a new structure of the device has been developed while a mounting technique for mounting electronic components has advanced, which results in a significantly higher density and a significantly higher speed in an electronic circuit.
However, there is a limitation to the communication speed of the electronic equipment as long as the electrical signal is conventionally transmitted and received. In this situation, recently, a necessary signal is transmitted and received as a light signal using an optical fiber.
Meanwhile, in a semiconductor field, a spherical semiconductor chip has been proposed and such a chip has been applied and developed in various fields including the high-density semiconductor device field and the medical field. For example, Ball Semiconductor, Inc. (Allen, Tex., US) has proposed that a semiconductor circuit is formed on a surface of a sphere of 1 mm diameter and such a spherical semiconductor circuit is applied in a microminiature electronic equipment such as a card-type electronic equipment (see U.S. Pat. No. 5,955,776 and U.S. Pat. No. 6,004,396). Further, various proposals have been made with respect to a technique for connecting the spherical semiconductor devices with each other and a technique for mounting the spherical semiconductor device on a wiring board directly (see Japanese Patent Kokai (Laid-Open) Publication Nos. 2000-216335 (FIG. 1) and 2000-349224 (FIG. 2)). Furthermore, a solar cell which employs the spherical semiconductor device has been also proposed (see Japanese Patent Kokai (Laid-Open) Publication No. 2001-185744). These intend to realize a higher speed and a miniaturization of the electronic circuit by using a spherical shape of the semiconductor device.